A model of the central mechanisms of male anuran acoustic behavior.

Abstract

Experiments on anuran acoustic mechanisms are described for Rana pipiens and two species of Hyla. These involve brain lesions, brain stimulations, and the recording of auditory responses from the medulla. These data, as well as data from the literature, are summarized and correlated in the form of a preliminary model of male anuran acoustic mechanisms. A motor coordination center, the efferent vocal center, in the region of the vagus and hypoglossal motor nuclei, is postulated. This is probably more or less equivalent to the expiratory and inspiratory centers - plus the additional mechanisms necessary to change respiratory mevements into calling movements. Electrically evoked release calling movements of the larynx and hyoid survive transections posterior to this region. Progressively more anterior transections result in progressively more abnormal and incomplete calling movements. A transection at the anterior edge of this area completely eliminates electrically evoked calling movements. Therefore, it appears that the efferent vocal center is responsible for generation of the motor patterns of vocalization. A sensory correlation center, the af ferent vocal center, in the region of the main sensory nucleus of the trigeminal, is postulated. This may be partly homologous to mammalian pontine respiratory centers. Electrically evoked release calling survives elimination of structures anterior, dorsal, and medial to this area; ablation of this area eliminates tactilely evoked release calling; and this is the area whose stimulation will most readily lead to release calling. The effects of brain lesions on mating calling are similar, except that the afferent vocal center must retain its connections with the preoptic area in order for calling to survive. Auditory responses were recorded from this region. More limited lesion and stimulation data suggest that the afferent vocal center may also be iuvolved in warning crying and inflating. Anatomical evidence shows that this area receives a great variety of sensory inputs. That the afferent vocal center is not directly involved in coordination of the motor patterns of calling is shown by the fact that release calling movements of the larynx and hyoid can often he evoked by electrical stimulation posterior to this area after it has been removed. Therefore, the afferent vocal center appears to analyze a variety of sensory inputs and to determine what, if any, respiration-derived behavior constitutes an appropriate response and is to be produced by the efferent vocal center.